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Check our curated list of full-stack, data structures & software architecture interview questions and answers for developers

Java interview questions

Java interview questions.

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  • 1.

    What are the two types of Exceptions in Java? Which are the differences between them?

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  • 2.

    What is JVM? Why is Java called the “Platform Independent Programming Language”?

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  • 3.

    What is the difference between an Applet and a Java Application?

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  • 4.

    What is the Difference between JDK and JRE?

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  • 5.

    What is a Servlet?

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  • 6.

    What is a JSP Page?

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  • 7.

    What are Directives?

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  • 8.

    What does System.gc() and Runtime.gc() methods do?

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  • 9.

    What differences exist between HashMap and Hashtable?

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  • 10.

    What is JDBC?

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  • 11.

    What does the “static” keyword mean? Can you override private or static method in Java?

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  • 12.

    What is the importance of finally block in exception handling?

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  • 13.

    What is the difference between Exception and Error in java?

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  • 14.

    When does an Object becomes eligible for Garbage collection in Java ?

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  • 15.

    What is an Iterator?

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  • 16.

    What are pass by reference and pass by value?

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  • 17.

    What is an Java Applet?

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  • 18.

    How HashMap works in Java?

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  • 19.

    What are the basic interfaces of Java Collections Framework?

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  • 20.

    What are the Data Types supported by Java? What is Autoboxing and Unboxing?

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  • 21.

    What is the difference between processes and threads?

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  • 22.

    What will happen to the Exception object after exception handling?

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  • 23.

    What is the difference between an Interface and an Abstract class?

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  • 24.

    What are Expressions?

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  • 25.

    What do you know about the big-O notation and can you give some examples with respect to different data structures?

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  • 26.

    What is Function Overriding and Overloading in Java?

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  • 27.

    How are the JSP requests handled?

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  • 28.

    What is the design pattern that Java uses for all Swing components?

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  • 29.

    What is the purpose Class.forName method?

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  • 30.

    What is the purpose of garbage collection in Java, and when is it used?

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  • 31.

    What’s the difference between sendRedirect and forward methods?

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  • 32.

    What are Decalarations?

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  • 33.

    What are JSP actions?

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  • 34.

    What is reflection and why is it useful?

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  • 35.

    Explain the architechure of a Servlet.

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  • 36.

    Explain Serialization and Deserialization.

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  • 37.

    How does Garbage Collection prevent a Java application from going out of memory?

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  • 38.

    How do I efficiently iterate over each entry in a Java Map?

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  • 39.

    What is a Constructor, Constructor Overloading in Java and Copy-Constructor?

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  • 40.

    What is the role of stub in RMI?

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  • 41.

    What is the difference between doGet() and doPost()?

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  • 42.

    What is the difference between GenericServlet and HttpServlet?

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  • 43.

    Explain the life cycle of a Servlet.

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  • 44.

    What is structure of Java Heap?

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  • 45.

    What differences exist between Iterator and ListIterator?

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  • 46.

    Explain the role of Driver in JDBC.

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  • 47.

    What is the relationship between an event-listener interface and an event-adapter class?

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  • 48.

    What is the applet security manager, and what does it provide?

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  • 49.

    What is the difference between throw and throws?

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  • 50.

    What happens when an applet is loaded?

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  • 51.

    When is the finalize() called? What is the purpose of finalization?

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  • 52.

    Can you access non static variable in static context?

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  • 53.

    What is a Server Side Include (SSI)?

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  • 54.

    Why Collection doesn’t extend Cloneable and Serializable interfaces?

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  • 55.

    Explain the life cycle of an Applet.

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  • 56.

    Which Swing methods are thread-safe?

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  • 57.

    What is the tradeoff between using an unordered array versus an ordered array?

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  • 58.

    What is Comparable and Comparator interface? List their differences.

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  • 59.

    What are untrusted applets?

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  • 60.

    What are the restrictions imposed on Java applets?

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  • 61.

    What is the difference between an Applet and a Servlet?

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  • 62.

    How does finally block differ from finalize() method?

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  • 63.

    What’s a deadlock?

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  • 64.

    What are Scriptlets?

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  • 65.

    What’s the difference between Enumeration and Iterator interfaces?

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  • 66.

    What is difference between ArrayList and LinkedList ?

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  • 67.

    What are the steps involved to make work a RMI program?

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  • 68.

    Does Java support multiple inheritance?

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  • 69.

    If an object reference is set to null, will the Garbage Collector immediately free the memory held by that object?

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  • 70.

    What is the importance of hashCode() and equals() methods?

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  • 71.

    Explain different ways of creating a thread. Which one would you prefer and why?

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  • 72.

    What is Java Priority Queue?

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  • 73.

    What is difference between fail-fast and fail-safe?

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  • 74.

    What is difference between Array and ArrayList ? When will you use Array over ArrayList?

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  • 75.

    What is the advantage of PreparedStatement over Statement?

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  • 76.

    What is meant by JSP implicit objects and what are they?

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  • 77.

    How threadsafe is enum in Java?

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  • 78.

    What are the differences between == and equals?

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  • 79.

    Is there anything like static class in java?

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  • 80.

    Compare the sleep() and wait() methods in Java

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  • 81.

    How and where are Annotations used in Java?

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  • 82.

    What is the difference between final, finalize and finally?

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  • 83.

    What is the main difference between StringBuffer and StringBuilder?

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  • 84.

    What’s the difference between a ClassNotFoundException and NoClassDefFoundError?

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  • 85.

    How can I synchornize two Java processes?

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  • 86.

    How do I break out of nested loops in Java?

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  • 87.

    What are the advantages of JSP?

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  • 88.

    What is the JIT?

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  • 89.

    What is a JavaBean exactly?

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  • 90.

    Can an enum be extended?

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  • 91.

    What is the Java Classloader?

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  • 92.

    What is the volatile keyword useful for?

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  • 93.

    What is the difference between HashMap, LinkedHashMap and TreeMap in Java?

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  • 94.

    What is the difference between public, protected, package-private and private in Java?

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  • 95.

    What's the advantage of using getters and setters?

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  • 96.

    What is static initializer?

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  • 97.

    Is Java “pass-by-reference” or “pass-by-value”?

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  • 98.

    Why does Java have transient fields?

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  • 99.

    What do the ... dots in the method parameters mean?

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  • 100.

    Can == be used on enum?

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  • 101.

    What is the use of CallableStatement? Name the method, which is used to prepare a CallableStatement.

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  • 102.

    How do I read/convert an InputStream into a String in Java?

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  • 103.

    What is Perm Gen space in Heap?

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  • 104.

    What is the difference between applets loaded over the internet and applets loaded via the file system?

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  • 105.

    What is the role of the java.rmi.Naming Class?

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  • 106.

    What is the purpose of using RMISecurityManager in RMI?

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  • 107.

    How do you ensure that N threads can access N resources without deadlock?

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  • 108.

    What are some of the best practices relating to the Java Collection framework?

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  • 109.

    What is meant by binding in RMI?

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  • 110.

    What is the role of Remote Interface in RMI?

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  • 111.

    What is the difference between a synchronized method and a synchronized block?

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  • 112.

    Explain the available thread states in a high-level.

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  • 113.

    What is the difference between Serial and Throughput Garbage collector?

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  • 114.

    What is the applet class loader, and what does it provide?

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  • 115.

    Explain Marshalling and demarshalling.

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  • 116.

    How do you find out what client machine is making a request to your servlet?

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  • 117.

    What is Servlet Chaining?

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  • 118.

    What is the basic principle of RMI architecture?

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  • 119.

    What does Connection pooling mean?

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  • 120.

    What is Double Brace initialization in Java?

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  • 121.

    How do I test a private function or a class that has private methods, fields or inner classes?

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  • 122.

    Why is char[] preferred over String for passwords?

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  • 123.

    What is RMI?

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  • 124.

    What exactly is marker interface in Java?

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  • 125.

    What are the differences between a HashMap and a Hashtable in Java?

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  • 126.

    When to use LinkedList over ArrayList in Java?

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  • 127.

    Why is Spring MVC better than Servlets / JSP ?

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  • 128.

    Explain a use case for the Builder Design Pattern

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  • 129.

    Does Java support default parameter values?

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  • 130.

    What is the main difference between an inner class and a static nested class in Java?

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  • 131.

    What is DGC ? And how does it work?

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  • 132.

    What is the difference between HashSet and TreeSet?

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  • 133.

    How does thread synchronization occurs inside a monitor? What levels of synchronization can you apply?

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  • 134.

    Does Garbage collection occur in permanent generation space in JVM?

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  • 135.

    What are the layers of RMI Architecture?

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  • 136.

    What does 'synchronized' mean?

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  • 137.

    What's wrong with Double Brace initialization in Java?

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  • 138.

    Why isn’t String‘s .length() accurate?

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  • 139.

    Compare volatile vs static variables in Java

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  • 140.

    What is an efficient way to implement a singleton pattern in Java?

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  • 141.

    What's the difference between SoftReference and WeakReference in Java?

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  • 142.

    Why ArrayList are preferable in many more use-cases than LinkedList?

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  • 143.

    Provide some examples when a finally block won't be executed in Java?

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  • 144.

    Is null check needed before calling instanceof?

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  • 145.

    Is it possible to call one constructor from another in Java?

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  • 146.

    Given two double values d1, d2, what is the most reliable way to test their equality?

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  • 147.

    Explain what will the code return

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7 Layering & Middleware interview questions for developers

Middleware in the context of distributed applications is software that provides services beyond those provided by the operating system to enable the various components of a distributed system to communicate and manage data. Middleware supports and simplifies complex distributed application...

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55 Docker interview questions and answers for software engineers

Docker is a set of platform as a service products that use OS-level virtualization to deliver software in packages called containers. Here is a list of coding interview questions on Docker to help you get ready for your next data structures interview in 2021.

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23 Databases interview questions and answers for software engineers

A database is an organized collection of data, generally stored and accessed electronically from a computer system. Where databases are more complex they are often developed using formal design and modeling techniques. Here is a list of coding interview questions on Databases to help you g...

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21 Concurrency interview questions and answers for software engineers

In computer science, concurrency is the ability of different parts or units of a program, algorithm, or problem to be executed out-of-order or in partial order, without affecting the final outcome. Here is a list of coding interview questions on Concurrency to help you get ready for your n...

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